In X-ray imaging, scattered radiation frequently causes a reduction in the image quality and the signal-to-noise ratio in the display of an examination object. The scattered radiation is caused, for example, by classical scattering or the so-called Compton effect. An important method for reducing scattered radiation is the use of focused antiscatter grids.
These are generally made from thin absorbing laminas, for example, from lead, with interspaces constructed from a well medium, and are arranged in the beam path of the X-radiation perpendicular to the direction of the latter. The absorber laminas are aligned substantially parallel to the X-radiation or in a fashion focused on to the X-ray focus in such a way that scattered radiation impinging at various angles is filtered out.
Simple antiscatter grids have a maximum line number of approximately 40 lines per centimeter and are usually moved linearly in a fashion perpendicular to the direction of incident radiation at a low speed over a portion of the image area in order not to be visible later on the X-ray image as a striped structure or artifact. There is a need in this case to control and trigger so as to ensure that the movement of the antiscatter grid is coordinated with the emission of the X-radiation and is started in good time before radiation begins.
As an alternative to a movement of the antiscatter grid, the striped structure or the artifact can be corrected by software in the later X-ray image. Using the simple moving antiscatter grid is impossible in the case of rapid, dynamic X-ray imaging methods, because of the rapid image sequence, while using the software correction is very expensive because of the long computing times. Dynamic X-ray imaging methods are understood, for example, as fluoroscopy, angiography, cardioangiography, and various 3-D recording methods.
If simple antiscatter grids with digital X-ray detectors are used, disturbing interference can arise between the regularly arranged absorbing laminas and the pixel structure of the digital X-ray detector, producing so-called Moiré structures. Multiline antiscatter grids that have a high number of, for example, 70 or more lines per centimeter have been developed in order to reduce these Moiré structures. The production of these multiline antiscatter grids is, however, very expensive and complicated, and it is therefore impossible to suppress striped structures or artifacts completely.